Reducing Forest Fuel Loads to Decrease Wildfire Risk

Reducing fuel load is one strategy forest owners can use to make their forests more resilient to fire. Moreover, the practices used to reduce fuel load also tend to make the forest more resistant to mortality from drought and bark beetles. Reduce the fuel load on your property by implementing the following practices:

Removing potential wildfire fuel, like these dried pine branches on a forest floor in the Catalina Mountains in Tucson, Arizona, is an important part of maintaining a healthy forest. Photo: Melanie Lenart

Clear small trees out of dense areas. Increase the height from the forest floor to the base of tree crowns by pruning branches, reducing the amount of debris directly below trees, and removing small trees that could otherwise carry fire into tree crowns. Taking these actions helps lessen the risk of a surface fire intensifying into a crown fire. Clearing small trees off the land also reduces competition for water during periods of drought. Not only can drought stress kill trees, but the lack of moisture needed to create pest-repelling sap makes it easier for bark beetles to get past a tree’s defenses.

Reduce the amount of fuel on the ground. Reducing excessive downed trees and other fuels diminishes fire risk. Removing slash from a site also limits the refuges available for bark beetles. Large logs typically contribute little to fire spread, so leaving two or three large logs or dead trees per acre can benefit wildlife and soils without tipping the wildfire equation toward high risk. Also, leaving a cover of some leaves and twigs can help retain soil moisture and nutrients.

Increase the spacing between trees. Thinning some of the existing trees out of overt dense forest stands reduces the chance that a fire that reaches the canopy will be able to spread through the tree crowns. Increasing light to the understory also may accelerate the decay of understory fuels. When selecting which trees to keep in the forest, favor the tallest, most structurally sound trees of those species most adapted to the site for the long term. Trees with forked tops, for instance, tend to be less structurally sound. Fire-resistant species vary by location. In western dry forests, ponderosa pines, western larches, and Douglas firs all have adaptations, such as thick bark and deep roots, that allow them to thrive under conditions of frequent surface fires. In contrast, lodgepole pines, spruces, true firs, and hemlock species have thin bark and shallow roots that make them susceptible to any kind of fire. Hardwood trees, especially deciduous ones such as maples, alders, and some oaks, also tend to be resistant to fire because of relatively high moisture levels in their leaves.

The following articles provide more information about reducing the risk of damaging fire in your forest: